Chris's approach is quite innovative and certainly ideal if a more complete and water-tight audit trail is your goal. However, since you seem to be aiming for a more "traditional" list of who changed what when, I would highly recommend Michael Woehrer's "History Class" posted on the OpenNTF code bin (here: http://www.openntf.org/Projects/codebin/codebin.nsf/CodeSearch/71E930683C3401A3C1256F2F00611BAA
The approach taken is to define a static array of field names and corresponding field labels in the PostOpen, and then use some other Lotusscript trickery to capture any changes in just those fields during that edit session. If you change a specific field multiple times, saving each time, only the final value will appear in the audit trail.
It works very well in the form demonstrated in the download database, but I wanted to be able to use a configuration document for each form to define which fields to track, rather than hard code the arrays element by element on the form itself. So I modified the code accordingly and encapsulated all of the form code into a subform that can be dropped on any form and "just work". If you'd like that code email me at kevin dot pettitt AT g mail dot com.
I will also be posting the code as part of a much larger OpenNTF project called "SuperNTF", so for those of you reading this in the future, you can check there as well,